The Use and Complications of Catheters for Hemodialysis Vascular Access: Introduction

Abstract

Venous catheters di€er from peripheral arteriovenous (AV) access devices in many important ways. This discussion focuses on their performance as a conduit for blood ¯ow between the patient and the dialyzer and on how catheter function is both limited and enhanced relative to the more common peripheral accesses. Catheter ¯ow is limited by the high resistance inherent in the extended length of venous catheters relative to dialysis needles, but the high rate of ¯ow in central veins also diminishes the opportunity for access recirculation. Cardiopulmonary recirculation is absent in patients with catheter access unless the patient also has a peripheral access. In the latter case, the same detrimental e€ect on urea clearance is seen regardless of which access device is used. Flow-dependent recirculation through circuits other than the peripheral AV access reduces the eciency of dialysis (regardless of the type of access, catheter, or peripheral AV device used) across both catheters and peripheral AV devices. The inside diameter of the catheter plays a sensitive role in determining catheter resistance to ¯ow. Slight increases in diameter under the same pressure head are associated with large increases in ¯ow. Negative pressure at the catheter in¯ow port generated by the blood pump is magni®ed relative to peripheral devices, predisposing to partial collapse of the pump tubing segment and erroneous blood ¯ow readings by the pump motor speed indicator. Setting a limit on prepump negative pressure can minimize this error. Future applications of dialysis may require lower pump speeds, which would allow more liberal use of catheter access if their potential for infection and clotting can be reduced.